Electronically controlled switch for an electric motor

ABSTRACT

A system in which the operation of an electric motor is controlled by electronically controlled switches. The system includes the motor having a run winding and a start winding, a heating component, and a motor control subsystem. A control unit closes a first switch to energize the run winding, closes a second switch to energize the start winding, determines based on an amplitude and a lag time of a current flowing through the motor whether the motor has started and is running normally, and if so, opens the second switch to de-energize the start winding and closes a third switch to activate the heating component. The control unit determines whether the motor has started and is running normally by comparing the real time amplitude and lag time of the current to a plurality of stored amplitudes and lag times associated with different operating conditions.

RELATED APPLICATION

The present non-provisional patent application claims priority benefitof an earlier-filed U.S. provisional patent application having the sametitle, Ser. No. 62/019,113, filed Jun. 30, 2014, and is a continuationand claims priority benefit of an earlier-filed U.S. non-provisionalpatent application having the same title, Ser. No. 14/752,242, filedJun. 26, 2015. The contents of the identified earlier-filed applicationsare hereby incorporated by reference into the present application as ifset forth in their entirety.

FIELD

The present invention relates to systems and methods for controlling theoperation of electric motors.

BACKGROUND

Electric motors that drive heavy loads require start windings totemporarily supplement run windings when starting. The de-energizing ofthe start winding once the electric motor has started is controlled by amechanical centrifugal switch located on the motor shaft, wherein thecentrifugal switch opens when the shaft reaches normal operating speed.In a clothes dryer, for example, the mechanical centrifugal switch hastwo sets of contacts, S1 and S2, that activate when the electric motorreaches a predetermined speed. S1 opens to de-energize the start windingwhich is no longer needed, and S2 closes to activate a heater circuit.The heater circuit is also controlled by other devices electricallyconnected in series with it in order to control the temperature of thedryer, but S2 ensures that the heater does not energize when theelectric motor is not spinning. Though simple and inexpensive,mechanical centrifugal switches suffer from several problems andlimitations, including that they have make noise when they open andclose and can be prone to manufacturing quality issues.

This background discussion is intended to provide information related tothe present invention which is not necessarily prior art.

SUMMARY

Embodiments of the present invention solve the above-described and otherproblems and limitations by providing a machine having an electric motorsystem in which the operation of an electric motor is controlled byelectronically controlled switches rather than a conventional mechanicalcentrifugal switch, thereby avoiding the noise and potentialmanufacturing quality issues associated with the use of the centrifugalswitch.

A machine constructed in accordance with an embodiment of the presentinvention may broadly comprise the electric motor system including anelectric motor having a run winding and a start winding, a heatingcomponent, and a motor control subsystem electrically connected to theelectric motor and the heating component and operable to control theiroperation. The motor control subsystem may include a control unit; auser interface in electrical communication with the control unit andoperable to receive a user input from a user and communicate the userinput to the control unit; a first electronically controlled switchelectrically connected in series between the control unit and the runwinding of the electric motor and operable to control a flow of electriccurrent to the run winding in response to a first control signal fromthe control unit; a second electronically controlled switch electricallyconnected in series between the control unit and the start winding ofthe electric motor and operable to control the flow of electric currentto the start winding in response to a second control signal from thecontrol unit; a voltage sensor in electrical communication with thecontrol unit and operable to sense a voltage being applied to theelectric motor and to provide a first input signal to the control unitregarding the sensed voltage, a current sensor in electricalcommunication with the control unit and electrically connected in serieswith the electric motor and operable to sense the electric currentflowing through the electric motor and to provide a second input signalto the control unit regarding the sensed current, and a thirdelectronically controlled switch electrically connected in seriesbetween the control unit and the heating component and operable tocontrol activation of the heating component in response to a thirdcontrol signal from the control unit.

The control unit may be operable to send the first control signal toclose the first electronically controlled switch and thereby energizethe run winding of the electric motor, send the second control signal toclose the second electronically controlled switch and thereby energizethe start winding of the electric motor, determine based on the firstand second input signals whether the electric motor has started, and ifthe electric motor has started, send a fourth control signal to open thesecond electronically controlled switch and thereby de-energize thestart winding of the electric motor. The control unit may be furtheroperable to determine based on the first and second input signalswhether the electric motor is operating normally, and if the electricmotor is operating normally, send the third control signal to close thethird electronically controlled switch and thereby activate the heatingcomponent.

In various implementations of the first embodiment, the machine mayfurther include any one or more of the following additional features.The machine may be a residential or commercial appliance, such as aclothes dryer. The electric motor may be an electric induction or apermanent magnet motor. The control unit may be a microprocessor. Thecurrent sensor may be a resistor, a transformer, or a Hall effectsensor. The motor control subsystem may further include a watchdogcircuit electrically connected to the third electronically controlledswitch and independently operable to open the third electronicallycontrolled switch to deactivate the heating component. The motor controlsubsystem may further include a mechanical thermal limiter located in anarea heated by the heating component and independently operable todeactivate the heating component if a temperature in the area heated bythe heating component exceeds a maximum temperature. The motor controlsubsystem may further include a fourth electronically controlled switchelectrically connected in series between the third electronicallycontrolled switch and the heating component and independently operableto control activation of the heating component in response to the thirdcontrol signal from the control unit. The motor control subsystem mayfurther include a temperature sensor located in an area heated by theheating component and in electrical communication with the control unitand operable to sense a temperature in the area heated by the heatingcomponent and to provide a third input signal to the control unitregarding the sensed temperature. The control unit may be operable todetermine based on the first and second input signals whether theelectric motor is operating normally by determining an amplitude and alag associated with the electric current and comparing the amplitude andthe lag to a plurality of stored amplitudes and lags associated withdifferent operating conditions. The first, second, and thirdelectronically controlled switches may be powered by the electric motor,wherein the first and second electronically controlled switches may benormally closed and the third electronically controlled switch may benormally open.

Additionally, each of these implementations and embodiments may bealternatively characterized as methods based on their functionalities.

This summary is not intended to identify essential features of thepresent invention, and is not intended to be used to limit the scope ofthe claims. These and other aspects of the present invention aredescribed below in greater detail.

DRAWINGS

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a schematic diagram of a first embodiment of a machineconstructed in accordance with the present invention;

FIG. 2 is a schematic diagram of a second embodiment of the machineconstructed in accordance with the present invention;

FIG. 3 is a block diagram of a motor control subsystem of the firstembodiment of the machine of FIG. 1;

FIG. 4 is a block diagram of the motor control subsystem of the secondembodiment of the machine of FIG. 2;

FIG. 5 is a flow diagram of steps involved in the operation of the motorcontrol subsystem of FIG. 4;

FIG. 6 is a flow diagram of substeps involved in the operation of themotor control subsystem of FIG. 4; and

FIG. 7 is a depiction of voltage and current signals associated with themotor control subsystems of FIGS. 3 and 4.

The figures are not intended to limit the present invention to thespecific embodiments they depict. The drawings are not necessarily toscale.

DETAILED DESCRIPTION

The following detailed description of embodiments of the inventionreferences the accompanying figures. The embodiments are intended todescribe aspects of the invention in sufficient detail to enable thosewith ordinary skill in the art to practice the invention. Otherembodiments may be utilized and changes may be made without departingfrom the scope of the claims. The following description is, therefore,not limiting. The scope of the present invention is defined only by theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features referred to are includedin at least one embodiment of the invention. Separate references to “oneembodiment”, “an embodiment”, or “embodiments” in this description donot necessarily refer to the same embodiment and are not mutuallyexclusive unless so stated. Specifically, a feature, structure, act,etc. described in one embodiment may also be included in otherembodiments, but is not necessarily included. Thus, particularimplementations of the present invention can include a variety ofcombinations and/or integrations of the embodiments described herein.

Broadly characterized, the present invention is a machine having anelectric motor system in which the operation of an electric motor iscontrolled by electronically controlled switches rather than aconventional mechanical centrifugal switch, thereby avoiding the noiseand potential manufacturing quality issues associated with the use ofthe centrifugal switch.

Referring to the figures, a machine 10 constructed in accordance withthe present invention is shown. Referring to FIG. 1, in a firstembodiment the machine 10 may broadly include an electric motor system12 having an electric motor 14 and a motor control subsystem 16.Referring also to FIG. 3, the motor control subsystem 16 may include acontrol unit 18; a user interface 20; first and second electronicallycontrolled switches 22,24; a voltage sensor 26; and a current sensor 28.In this first embodiment, the machine 10 may be substantially anymachine incorporating the electric motor 14. The electric motor 14 mayinclude a run (or main) winding 32 which is sufficient to drive theelectric motor 14 during normal operation, and a start winding 34 whichprovides temporary supplementary driving force during starting of theelectric motor 14. The electric motor 14 may be an electric induction orpermanent magnet motor. For example, the electric motor 14 may be athree-phase, four-pole alternating current (AC) induction or permanentmagnet motor rated to operate at a maximum voltage of approximatelybetween 190 Volts and 200 Volts and a maximum current of approximatelybetween 4 Amps and 6 Amps. The electric motor 14 may drive anyappropriate load. For example, the electric motor 14 may drive a fan,pump, blower, or rotating drum, which may be part of a residential orcommercial appliance, such as a clothes dryer or oven, or a heating andair-conditioning unit, which may include additional electrical ormechanical components not described herein.

The motor control subsystem 16 may be broadly operable to controloperation of the electric motor 14, including during starting and duringnormal operation. The control unit 18 may be operable to receive inputsignals from the user interface 20 and the sensors 26,28 and generatecontrol signals for the first and second electronically controlledswitches 22,24. The control unit 18 may be a microprocessor having amemory or able to access a memory. The user interface 20 may be inelectrical communication with the control unit 18 and operable toreceive input from a user (such as, e.g., to start the electric motor14) and communicate that input to the control unit 18.

The first electronically controlled switch 22 may be electricallyconnected in series between the control unit 18 and the run winding 32of the electric motor 14 and operable to control the flow of electriccurrent to the run winding 32 in response to a first control signal fromthe control unit 18. The second electronically controlled switch 24 maybe electrically connected in series between the control unit 18 and thestart winding 34 of the electric motor 14 and operable to control theflow of electric current to the start winding 34 in response to a secondcontrol signal from the control unit 18.

The voltage sensor 26 may be in electrical communication with thecontrol unit 18 and operable to sense a voltage being applied to theelectric motor 14 and to provide a first input signal to the controlunit 18 regarding the sensed voltage. The current sensor 28 may be inelectrical communication with the control unit 18 and electricallyconnected in series with the electric motor 14 and operable to sense theelectric current flowing through the electric motor 14 and to provide asecond input signal to the control unit 18 regarding the sensed current.The current sensor 28 may be a resistor, a transformer, a Hall effectsensor, or other suitable current-sensing device.

Referring to FIG. 2, in a second embodiment the machine 10 may broadlyinclude the electric motor system 12 having the electric motor 14, themotor control subsystem 16, and a heating component 42. Referring alsoto FIG. 4, the motor control subsystem 16 may include the control unit18; the user interface 20; the first and second electronicallycontrolled switches 22,24; the voltage sensor 26; the current sensor 28;third and fourth electronically controlled switches 38,40; and atemperature sensor 44. In this second embodiment, the machine 12 may bea clothes dryer, oven, heating unit or substantially any residential orcommercial machine incorporating the electric motor 14 and the heatingcomponent 42.

The third electronically controlled switch 38 may be electricallyconnected in series between the control unit 18 and the heatingcomponent 42 and operable to control activation of the heating component42 in response to a third control signal from the control unit 18. Thethird electronically controlled switch 38 may be further controlled by awatchdog circuit 46 operable to open the electronically controlledswitch 38 if the control unit 18 fails. Additionally, a mechanicalthermal limiter 48 may be located in an area heated by the heatingcomponent 42 and electrically connected in series with the heatingcomponent 42 and operable to deactivate the heating component 42 if thetemperature in the area exceeds a maximum temperature. In addition or asan alternative to the watchdog circuit 46 and/or mechanical thermallimiter 48, the fourth electronically controlled switch 40 may beelectrically connected in series between the third electronicallycontrolled switch 38 and the heating component 42 and operable tocontrol activation of the heating component 42 in response to the samethird control signal from the control unit 18, thereby providingredundancy in case the third electronically controlled switch 38 failsto open when required to do so.

The various electronically controlled switches 22,24,38,40 may berelays, triacs, or other types of electronically controlled switches.For example, if the electric motor 14 draws 30 Amps, then theelectronically controlled switches 22,24,38,40 may be 1 Watt relays.Furthermore, the electronically controlled switches 22,24,38,40 may beof different types. For example, the second electronically controlledswitch 24 may be a less robust type than the first electronicallycontrolled switch 22 because the first electronically controlled switch22 carries most of the electric current flowing to the electric motor14.

The heating component 42 is operable to generate heat, such as when usedin a clothes dryer, oven, or heating unit. The heating component 42 mayuse electricity, gas, or other technology to generate the heat. Thetemperature sensor 44 may be in electrical communication with thecontrol unit 18 and located in an area heated by the heating component42 and operable to sense the temperature created by the heatingcomponent 42 and to provide an input signal to the control unit 18regarding the sensed temperature. The temperature sensor 44 may be athermistor or other temperature-sensing device.

Operation of the electric motor system 12 will be described with respectto the second embodiment as the first embodiment operates substantiallythe same except with regard to the additional components of the secondembodiment. Referring to FIG. 5, the control unit 18 may receive inputfrom the user via the user interface 20 to start the machine 10, inwhich case the control unit 18 sends the first and second controlsignals to close the first and second electronically controlled switches22,24 and thereby energize the run and start windings 32,34 to cause theelectric motor 14 to try to start, as shown in step 100. The controlunit 18 receives input signals from the voltage and current sensors26,28 and, based thereon, determines whether the electric motor 14 hassuccessfully started, as shown in step 102. If the control unit 18determines that the electric motor 14 has not successfully started andis not running at the correct speed, the control unit 18 re-sends thesecond control signal to close the second electronically controlledswitch 24 and thereby re-energize the start winding 34, as shown in step100. After several unsuccessful attempts to start the electric motor 14and bring it to the correct speed, the control unit 18 may send controlsignals to open both the first and second electronically controlledswitches 22,24 and thereby shut off the electric motor 18. If thecontrol unit 18 determines that the electric motor 14 has successfullystarted, then it sends the fourth control signal to cause the secondelectronically controlled switch 24 to open and thereby de-energize thestart winding 34, as shown in step 104, and the electric motor 14thereafter runs normally on the run winding 32. The control unit 18continues receiving the first and second input signals from the voltageand current sensors 26,28 and, based thereon, determines whether theelectric motor 14 is running normally, as shown in step 106. If thecontrol unit 18 determines that the electric motor 14 is runningnormally, then it sends the third control signal to close the third andfourth electronically controlled switches to activate the heatingcomponent 42, as shown in step 108. If the control unit 18 detectsabnormal operation, then it takes appropriate action, as shown in step110, which may include restarting or shutting off the electric motorand/or deactivating the heating component.

With regard to the control unit 18 using the sensed voltage and currentinformation to monitor the operation of the electric motor 14, theelectric motor system 12 may function as follows. Referring to FIG. 6,the control unit 18 receives the first input signal from the voltagesensor 26, as shown in step 200, which synchronizes the control unit 18to the AC line voltage being applied to the electric motor 14. Thecontrol unit 18 receives the second input signal from the current sensor28, as shown in step 202. Referring also to FIG. 7, the load on theelectric motor 14 has some inductance which causes the current throughthe electric motor 14 to lag the voltage applied to the electric motor14. The current amplitude 50 and current lag 52 is different duringstart-up, normal running, and abnormal operations (e.g., a locked rotor,an open winding, or other fault). These different current amplitudes andlag times may be pre-determined and stored in a look-up table in amemory that is part of or accessible to the control unit 18. Thedifferent current amplitudes and lag times may be determined for theindividual electric motor or for the type of the electric motor, and ifthe latter, may take into account various manufacturing and/oroperational tolerances for the type for the electric motor that mightmake different individual electric motors of the same type exhibitslightly different current amplitudes and lag times under the samecircumstances. During all phases of electric motor operation (e.g.,starting, running, stopping), the control unit 18 constantly comparesthe real time current amplitude and current lag with these patternsstored in memory, as shown in step 204. Based on those comparisons, thecontrol unit 18 determines whether the electric motor 14 is runningnormally or abnormally, as shown in step 206, and if the electric motor14 is running abnormally, the control unit 18 takes appropriate action(e.g., restart, shut-off, error signal), as shown in step 208.

In various implementations, one or more of the electronically controlledswitches 22,24,38,40 may be physically located on the same circuit boardas the control unit 18 and may share the same power supply as thecontrol unit 18, one or more of the electronically controlled switches22,24,38,40 may be physically located intermediate between the controlunit 18 (i.e., not on the same circuit board as the control unit 18) andthe electric motor 14, one or more of the electronically controlledswitches 22,24,38,40 may be physically located in close proximity to oron the electric motor 14 and may share the same power supply as theelectric motor 14, or any combination thereof.

In one implementation, the electric motor (rather than the AC linevoltage) may power one or more of the electronically controlled switches22,24,38,40. In this implementation, the third electronically controlledswitch 38 may be normally open (so if power is lost, it opens andde-activates the heating component 42), and the first and secondelectronically controlled switches 22,24 may be normally closed (so thatthe electric motor 14 can be started).

In one implementation, a speed sensor may be used in place of thevoltage and current sensors 26,28 to provide input to the control unit18. In this implementation, the speed sensor is used to measure theelectric motor's speed, such that when the electric motor 14 reaches apredetermined speed, the second electronically controlled switch 24 isopened to de-energize the start winding 34, and the third and fourthelectronically controlled switches 38,40 are closed to activate theheating component 42. Thereafter, the control unit 18 may monitor thespeed sensor to determine whether the electric motor 14 is operating atthe proper speed, and if it is not, take appropriate action. The speedsensor may be, for example, a Hall effect sensor, an optical sensor, orother speed-sensing device.

Thus, the present invention provides advantages over the prior art,including that it provides the machine 10 having the electric motorsystem 12 in which the operation of the electric motor 14 is controlledby the electronically controlled switches 22,24,38,40 rather than aconventional mechanical centrifugal switch, thereby avoiding the noiseand potential manufacturing quality issues associated with the use ofthe centrifugal switch.

Although the invention has been described with reference to the one ormore embodiments illustrated in the figures, it is understood thatequivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

Having thus described one or more embodiments of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A motor control subsystem for an electric motor systemincluding an electric motor having a run winding and a start winding andfurther including a user interface configured to receive a user inputfrom a user, the motor control subsystem being configured to controloperation of the electric motor, the motor control subsystem comprising:a control unit in electrical communication with the user interface andconfigured to receive the user input from the user interface; a firstelectronically controlled switch electrically connected in seriesbetween the control unit and the run winding of the electric motor andconfigured to control a flow of electric current to the run winding inresponse to a first control signal from the control unit; a secondelectronically controlled switch electrically connected in seriesbetween the control unit and the start winding of the electric motor andconfigured to control the flow of electric current to the start windingin response to a second control signal from the control unit; and asensor in electrical communication with the control unit and configuredto sense a voltage or a current to the electric motor and to provide aninput signal to the control unit regarding the sensed voltage orcurrent, wherein the control unit sends a first control signal to closethe first electronically controlled switch and thereby energize the runwinding of the electric motor, sends a second control signal to closethe second electronically controlled switch and thereby energize thestart winding of the electric motor, determines based on the inputsignal whether the electric motor has started, and if the electric motorhas started, sends a third control signal to open the secondelectronically controlled switch and thereby de-energize the startwinding of the electric motor.
 2. The motor control subsystem as setforth in claim 1, wherein the machine is a residential or commercialappliance.
 3. The motor control subsystem as set forth in claim 2,wherein the machine is a clothes dryer.
 4. The motor control subsystemas set forth in claim 1, wherein the electric motor is an electricinduction or a permanent magnet motor.
 5. The motor control subsystem asset forth in claim 1, wherein the control unit is a microprocessor. 6.The motor control subsystem as set forth in claim 1, wherein the sensoris selected from the group consisting of a resistor, a transformer, aHall effect sensor.
 7. The motor control subsystem as set forth in claim1, wherein the control unit is located on a printed circuit board andreceives power from a first power supply, and the electric motorreceives power from a second power supply, and the first and secondelectronically controlled switches are located on the printed circuitboard and receive power from the first power supply.
 8. The motorcontrol subsystem as set forth in claim 1, wherein the control unitreceives power from a first power supply, and the electric motorreceives power from a second power supply, and the first and secondelectronically controlled switches are located on the electric motor andreceive power from the second power supply.
 9. A motor control subsystemfor an electric motor system including an electric motor having a runwinding and a start winding and further including a heating componentand a user interface configured to receive a user input from a user, themotor control subsystem being configured to control operation of theelectric motor and the heating component, the motor control subsystemcomprising: a control unit in electrical communication with the userinterface and configured to receive the user input from the userinterface; a first electronically controlled switch electricallyconnected in series between the control unit and the run winding of theelectric motor and configured to control a flow of electric current tothe run winding in response to a first control signal from the controlunit; a second electronically controlled switch electrically connectedin series between the control unit and the start winding of the electricmotor and configured to control the flow of electric current to thestart winding in response to a second control signal from the controlunit; a sensor in electrical communication with the control unit andconfigured to sense a voltage or a current to the electric motor and toprovide an input signal to the control unit regarding the sensed voltageor current; and a third electronically controlled switch electricallyconnected in series between the control unit and the heating componentand configured to control activation of the heating component inresponse to a third control signal from the control unit, wherein thecontrol unit is configured to send a first control signal to close thefirst electronically controlled switch and thereby energize the runwinding of the electric motor, send a second control signal to close thesecond electronically controlled switch and thereby energize the startwinding of the electric motor, determine based on the input signalwhether the electric motor has started, and if the electric motor hasstarted, send a third control signal to open the second electronicallycontrolled switch and thereby de-energize the start winding of theelectric motor, and wherein the control unit is further configured todetermine based on the signal whether the electric motor is operatingnormally, and if the electric motor is operating normally, send a fourthcontrol signal to close the third electronically controlled switch andthereby activate the heating component.
 10. The motor control subsystemas set forth in claim 9, wherein the machine is a residential orcommercial appliance.
 11. The motor control subsystem as set forth inclaim 10, wherein the machine is a clothes dryer.
 12. The motor controlsubsystem as set forth in claim 9, wherein the electric motor is anelectric induction or a permanent magnet motor.
 13. The motor controlsubsystem as set forth in claim 9, wherein the control unit is amicroprocessor.
 14. The motor control subsystem as set forth in claim 9,wherein the sensor is selected from the group consisting of a resistor,a transformer, a Hall effect sensor.
 15. The motor control subsystem asset forth in claim 9, further including a watchdog circuit electricallyconnected to the third electronically controlled switch andindependently configured to open the third electronically controlledswitch to deactivate the heating component.
 16. The motor controlsubsystem as set forth in claim 9, further including a mechanicalthermal limiter located in an area heated by the heating component andindependently configured to deactivate the heating component if atemperature in the area heated by the heating component exceeds amaximum temperature.
 17. The motor control subsystem as set forth inclaim 9, further including a fourth electronically controlled switchelectrically connected in series between the third electronicallycontrolled switch and the heating component and independently configuredto control activation of the heating component in response to the thirdcontrol signal from the control unit.
 18. The motor control subsystem asset forth in claim 9, further including a temperature sensor located inan area heated by the heating component and in electrical communicationwith the control unit and configured to sense a temperature in the areaheated by the heating component and to provide a third input signal tothe control unit regarding the sensed temperature.
 19. The motor controlsubsystem as set forth in claim 9, wherein the control unit isconfigured to determine based on the input signal whether the electricmotor is operating normally by determining an amplitude and a lag timeassociated with the electric current and comparing the amplitude and thelag time to a plurality of stored amplitudes and lags times associatedwith different operating conditions.
 20. The motor control subsystem asset forth in claim 9, wherein the first, second, and thirdelectronically controlled switches are powered by the electric motor,and wherein the first and second electronically controlled switches arenormally closed and the third electronically controlled switch isnormally open.
 21. A method of controlling an electric motor system, theelectric motor system including an electric motor having a run windingand a start winding and a motor control subsystem, the motor controlsubsystem including a control unit, first and second electronicallycontrolled switches, and a sensor, the method comprising the steps of:(1) sending by the control unit a first control signal to close thefirst electronically controlled switch and thereby energize the runwinding of the electric motor; (2) sending by the control unit a secondcontrol signal to close the second electronically controlled switch andthereby energize the start winding of the electric motor; (3) receivingat the control unit an input signal from the sensor regarding a voltageor a current to the electric motor; (4) determining by the control unitbased on the input signals whether the electric motor has started; and(5) if the electric motor has started, sending by the control unit athird control signal to open the second electronically controlled switchand thereby de-energize the start winding of the electric motor.
 22. Themethod as set forth in claim 21, wherein the machine is a residential orcommercial appliance.
 23. The method as set forth in claim 22, whereinthe machine is a clothes dryer.
 24. The method as set forth in claim 21,wherein the electric motor is an electric induction or a permanentmagnet motor.
 25. The method as set forth in claim 21, wherein thecontrol unit is a microprocessor.
 26. A method of controlling anelectric motor system, the electric motor system including an electricmotor having a run winding and a start winding, a heating component, anda motor control subsystem, the motor control subsystem including acontrol unit, first, second, and third electronically controlledswitches, and a sensor, the method comprising the steps of: (1) sendingby the control unit a first control signal to close the firstelectronically controlled switch and thereby energize the run winding ofthe electric motor; (2) sending by the control unit a second controlsignal to close the second electronically controlled switch and therebyenergize the start winding of the electric motor; (3) receiving at thecontrol unit an input signal from the sensor regarding a voltage or acurrent to the electric motor; (4) determining by the control unit basedon the input signal whether the electric motor has started; (5) if theelectric motor has started, sending by the control unit a third controlsignal to open the second electronically controlled switch and therebyde-energize the start winding of the electric motor; (6) determining bythe control unit based on the input signal whether the electric motor isoperating normally; and (7) if the electric motor is operating normally,sending by the control unit a fourth control signal to close the thirdelectronically controlled switch and thereby activate the heatingcomponent.
 27. The method as set forth in claim 26, wherein the step (6)of determining whether the electric motor is operating normallyincludes— determining by the control unit based on the input signal anamplitude and a lag time associated with the electric current; comparingby the control unit the amplitude and the lag time to a plurality ofstored amplitudes and lag times associated with different operatingconditions.
 28. The method as set forth in claim 26, wherein the machineis a residential or commercial appliance.
 29. The method as set forth inclaim 28, wherein the machine is a clothes dryer.
 30. The method as setforth in claim 26, wherein the electric motor is an electric inductionor a permanent magnet motor.
 31. The method as set forth in claim 26,wherein the control unit is a microprocessor.